Indeed, Black Flash was the one to defeat Savitar. The battle was full of action and unexpected twists, but in the end, Black Flash emerged victorious.
The way Flash defeats Savitar in comics involves a lot of factors. He figures out Savitar's patterns, discovers a hidden flaw in his powers, and then strikes at the right time with maximum speed and precision.
When Savita explained the concept of time travel, he meant that time travel was a way to travel through time, and time travel referred to a way to extend the state of a timeline from one moment to another in order to avoid the paradox and uncertainty of time travel. To be specific, time travel could directly change the state of the timeline through the occurrence of an event or the entry of an entity, thus avoiding many common problems and contradictions in time travel.